GnRH has been shown to play a role in the regulation of human chorionic gonadotropin (CG) secretion by the human placenta. Molecular studies have also demonstrated that human placental trophoblast cells synthesize a pro-gonadotropin releasing hormone (pro-GnRH) identical to human hypothalamic pro-GnRH (Duello et al., Endocrinology 133 2617, 1993). Far less is known in non-human primates. Seshagiri et al. have shown an immunoreactive GnRH to be produced by blastocysts during the peri-attachment period and by placental cytotrophoblast cells in the rhesus monkey (Macaca mulatta) (Human Reprod 9 1300, 1994). A gene amplification/sequence analysis study was undertaken to determine whether placental pro-GnRH produced by the rhesus monkey is identical to its human placental counterpart. Total RNA was prepared from first trimester placental tissue (36 d) (Dr. T. Golos), reverse transcribed, and pro-GnRH cDNA amplified using primers based on the sequence of human hypothalamic/placental pro-GnRH. The amplified transcript (single band of ~198 bp) was ligated into pCRtmII vector, transformed into TOP10 F' cells, and cloned (Invitrogen Corp., San Diego, CA). Positive clones were expanded, plasmid DNA isolated and analyzed by restriction digestion, and colonies producing the expected 198 bp transcript identified. Sequence analysis revealed rhesus monkey placental pro-GnRH to be 96% homologous to its human placental counterpart. A single base difference in the domain encoding GnRH proper results in the same amino acid in position 8 (Arg). Seven base differences in the domain encoding the GnRH-associated peptide (GAP) resulted in seven different amino acids. Only one of these differences - proline instead of lysine in position 68 - resulted in a 'deletion' of a basic amino acid, which would denote a probable cleavage site. However, because there is a lysine in position 67 (69 amino acids total), this difference may not be physiologically or phylogenetically significant. These studies have established that placental GnRH in the rhesus monkey is identical to its human placental counterpart, thus supporting the use of synthetic 'mammalian' GnRH in studies of regulation of monkey CG. In addition, the unique sequence of GAP peptides within the pro-GnRH molecule have been identified. While the role of GAP peptides in pituitary function are unclear, their role in placental function is totally unexplored and a topic of further study. Key words